Our project is a longitudinal study investigating the relationship between the physiological and psychological characteristics and behaviors of drug-abusing parents (on methadone) and the behavioral and physiological functioning of their offspring infants. Etiological factors affecting infants' development may be of toxicological, genetic, or social/environmental nature: (a) Toxicological--drug(s) used by mother during pregnancy may have toxic effects on the growing fetus, and hence, on the infant's development. (b) Genetic--mothers or fathers may exhibit a genetically transmittAble neurophysiological dysfunction which may manifest itself during adulthood in the form of drug abuse, but is preceded during childhood by symptoms of attentional deficits and hyperactivity. (c) Social/environmental--the quality of parents' interaction with their infants may significantly affect their offspring's development. We interview the parents during pregnancy and test them on a variety of behavioral and physiological measures, then after delivery we see their infants six times until the age of two years. We examine the infants' behavioral, motoric, physiological, and social responses, and we observe the infants' interaction with their mothers (and fathers when possible).